Hi Izzy,
To help narrow this down, could you confirm whether the verification request appears before the Windows desktop loads or after you have already signed in? What is the exact wording of the message and is this a personal laptop or one managed by your workplace or school? Please hide your phone number, email address and verification code if you share a screenshot.
If the message appears after reaching the desktop, please check Settings > Accounts > Email & accounts and Settings > Accounts > Access work or school. Let me know if you see an old, duplicate or unfamiliar account listed there. If the laptop is managed by an organization, do not disconnect anything yet, as the verification requirement may be controlled by its security policy.
These details should help identify whether the request is coming from the Windows sign-in screen or another account connected to the laptop.